I understand how hurtful it was, but please look at it through the lens of her BPD. It can be hard to understand how a mind like that works unless you've intimately known people who were. Part of it was trying to grab attention, no doubt. But a bigger part of it was that she has a poor concept of identity; that lies at the heart of BPD. The way they view themselves can change 180 degrees in a matter of minutes with little external provocation that anyone else would notice. They don't become that way unless they experienced severe trauma and instability as very tiny children, before a stable sense of self had the chance to form.

Again, I'm sorry for the pain this has caused you. There's so much misunderstanding and stigma around gender transitioning, and such things only add to it. 15 years is a long time to struggle with being able to finally be yourself. I'm so glad you were able to reach out for help.